Protective coating



United States Patent 3,274,032 PROTECTIVE COATING Richard L. Every, Ralph Le Roy Grimsley, and Olen L. Riggs, Jr., Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Oklahoma No Drawing. Filed Dec. 20, 1963, Ser. No. 332,285

11 Claims. (Cl. 1486.14)

The present invention relates to surface coating and, in one aspect, the present invention relates to the prep aration of corrosion resistant coverings on metal surfaces.

It is an object of the present invention to provide a surface coating for an article.

It is another object of the present invention to provide a corrosion resistant surface coating for an article.

It is an additional object of the present invention to provide a corrosion resistant coating for a metal surface.

Yet another object of the present invention is to provide a method for removing ferrous deposits on the surface of a metal article and to substitute in the place of such deposits, a coating which is relatively inert with respect to oxygen.

Still another object of the present invention is to provide a corrosion resistant surface on a metal workpiece, which surface may be subsequently covered with paint, lacquer, and the like.

Other and additional objects of the present invention will become apparent from a reading of the following specification.

In one aspect, the present invention may be said to reside in a method for forming a corrosion resistant coating on a metal surface which comprises the step of contacting the metal object with a solution comprising an effective amount of a strong, monoxidizing acid and an effective amount of a nitrobenzaldehyde or a ring-substituted lower alkyl derivative thereof, together with a suitable nitrobenzaldehyde solvent.

In another aspect, the present invention may be said to reside in a solution for treating surfaces, which solution comprises an effective amount of a strong, nonoxidizing acid and an effective amount of a nitrobenzaldehyde, or a ring-substituted lower alkyl derivative thereof in a nitrobenzaldehyde solvent.

As used herein, the term a nitrobenzaldehyde is intended to include only the two isomers, meta and para nitrobenzaldehyde. Moreover, the term lower alkyl derivative thereof is intended to include only soluble forms of the above isomeric nitrobenzaldehydes having lower alkyl groups attached to the benzene ring. By lower alkyl is meant hydrocarbon radicals preferably saturated, and preferably having not more than about three carbon atoms. If more than one alkyl radical is present, the total number of carbon atoms in all such radicals is preferably not more than about four. Suitable examples of such compounds are: benzaldehyde; tetramethyl m-, -isopropyl, 3-nitrobenzaldehyde; 5- methyl, 3-nitrobenzaldehyde and 4-nitro, S-rhethyl m-toluic aldehyde. Generally meta and para nitrobenzaldehyde are preferred to their lower alkyl derivatives for the purposes of this invention, and of these para is most preferable.

An important feature of the present invention is the utilization of a strong, nonoxidizing acid, either mineral or organic, in the coating solution. As used herein, the term strong acid is inclusive of all acids having a first hydrogen dissociation constant of about 0.1 or more, and preferably those having a dissociation constant of from about 0.2 to about 1.0. Additionally, the term nonoxidizing as used herein includes those acids which do not oxide the metals being treated under solution conditions. Examples of suitable strong, nonoxidizing acids which may be used in conjunction with the present invention are: hydrogen chloride, sulfuric acid, sulfurous acid, phosphoric acid, bromic acid, trichloroacetic acid, picric acid and perchloric acid. Of these, hydrochloric acid and sulfuric acid are preferred.

A wide variety of benzaldehyde solvents may also be utilized in conjunction with the practice of the present invention. In general, it may be said that any material in which the benzaldehyde, or its derivative, is soluble under existing conditions is suitable for use as a solvent so long as the solvent is compatible with the other constituents of the solution. Examples of materials which may be utilized as solvents are the alcohols having from one to about 12 carbon atoms, acetone, N,N-dimethylformamide, N,N-diethylformamide, formamide and dioxane. Preferably, ethanol or acetone are utilized.

There is no criticality to the sequence in which the various components are added together to form the protective solution; that is to say, the acid, benzaldehyde and solvent may be added simultaneously to an empty container or these components may be added in any particular sequence desired. In general, it will be found most satisfactory to add the benzaldehyde to the solvent prior to the addition of the acid. By this means, it is possible to insure complete solution of the benzaldehyde.

In addition to the noncritical nature of the sequence in which the individual components are added to prepare the solution, the exact proportions of such components within the solution are likewise not particularly critical. For instance, it has been found that from about 1000 to about 3000 parts of the inhibitor per million parts of the final solution is, under ordinary circumstances, quite satisfactory. Within this range, it is ordinarily preferred to use from about 2500 to about 3000 parts of inhibitor per million parts of the solution, although it is stressed again that these concentration ranges are not critical and concentrations of inhibitor outside them may be expected to produce some advantage. The acid concentration in the final solution is likewise not critical. In general from about 0.1 to about 3.0 normal concentration of the acid in the final solution is satisfactory. Here again, however, values outside this range produce some improvement. Within the range, from about 0.25 to about 1.0 normal is ordinarily preferred and, in general, an acid concentration of about 0.5 normal will most usually be used.

After the solution has been prepared, it is then utilized for forming a corrosion resistant surface on metal objects. As used herein, the term metal includes any of the metals which are normally corroded in the presence of water vapor or oxygen. Included in this group are the various ferrous metals, such as, iron, plain carbon steels of low, medium and high carbon content, cast irons and alloy steels, including high alloy content steels, ferritic and austenitic steels and the like. In addition, this invention may be utilized, with some success, for the protection of various nonferrous metals, such as, copper, aluminum, etc. and the nonferrous alloys of these materials. Couples of dissimilar metals may also be protected by the use of the present invention. For instance, couples of steels with copper, aluminum, nickel, chromium and alloys of these metals may be treated according to the teachings of the present invention to produce a coat ing thereon which is substantially inert with respect to water vapor and/or oxygen.

In one method for treating metals, a solution containing the three components discussed above is placed in a chemically inert container at a depth sufiicient to completely emerse the portion of the object to be treated. Thereupon the desired portion of the object is placed in the container below the surface of the solution and is al- Patented Sept. 20, 1966 lowed to remain there a period of time. In general, any such emersion will have useful effect toward the formation of a protective coating. However, it is usually preferred to allow the objects being treated to remain emersed in the solution for at least thirty minutes and ordinarily not less than four hours. Moreover, in general, little additional advantage is obtained from allowing such objects to remain in the solution for more than about 16 hours, although no deleterious effects are realized from the emersion of such objects longer than this time. Thus, it is ordinarily preferred to allow the object being treated to remain in contact with the solution from about four to about 16 hours. The temperature of the solution bath is also not critical and will ordinarily be ambient temperature. In general, the only factors limiting upper temperature are the same factors limiting the stability of the solution itself; that is to say, the solution may be maintained at any temperature at which the constituents of the solution do not break down from thermal decomposition, provided such temperature is above the freeze point of the solution.

After the metal objects have remained in the solution the desired length of time, they are then removed and wiped clean whereupon they are ready for use.

In order to demonstrate the utility and methods of application of the present invention, the following examples are presented. In these examples, reference will be made to test coupons which, unless otherwise specified, are mild steel rods approximately 8 inches long and approximately inch in diameter. Moreover, in each of the examples, the various solutions which are utilized were prepared by dissolving the benzaldehyde in the solvent and then adding the acid solution. In all cases, the temperature of the bath was ambient temperature, that is, approximately 23 C.

Example I A 1 inch by 3 inch by 0.070 inch bright, mild steel coupon was placed in a solution consisting of 400 ml. of a 0.5 N hydrochloric acid, 1.25 grams of p-nitrobenzaldehyde and 25 ml. of 100% ethanol. The coupon was left in the solution for 16 hours and was then removed, rinsed in tap water and wiped thoroughly with a dry cloth. The coupon was observed to possess a smooth, reddish brown coating.

After remaining in the atmosphere for 90 days, no corrosion was observed on the surface of the coupon thus treated.

The above procedure was repeated utilizing a rusty coupon of the same type. As in the case of the bright coupon, a smooth, reddish brown coating was observed on the previously rusty coupon when it was removed from the solution and the coupon was observed to be free from corrosion at the end of an exposure of 90 days to the atmosphere.

Example 11 The procedure of Example I was repeated utilizing a rusty and a bright, mild steel coupon in a solution wherein the inhibitor was ortho-nitrobenzaldehyde rather than the para-nitrobenzaldehyde used in Example I.

At the end of an emersion of 16 hours, no protective film was observed on the surface of either the rusty or the bright coupon.

Example III The procedure of Example 11 was repeated utilizing meta-nitrobenzaldehyde in the place of the ortho-nitrobenzaldehyde utilized in Example II.

At the end of an emersion of 16 hours in the solution, a smooth, uniform, gray coating was observed on both the rusty and the bright coupons.

At the end of an exposure of 90 days to the atmosphere, no corrosion or rust was observed on the surface of either the previously rusty or the previously bright coupons.

4.- Example IV Solutions were prepared utilizing 1.25 grams of each of the inhibitors, ort-ho, meta and para, benzaldehyde. In addition, each of these solutions also contained 25 ml. of ethyl alcohol and 400 ml. of water which was substituted in the place of the acid previously used. Into each of these solutions, a rusty and a bright coupon were emersed for a period of 16 hours.

At the end of that time, the coupons were removed from each of the solutions and the surface of each of the coupons was observed to be rusty and pitted, with no protective coating formed thereon.

Example V Solutions were prepared utilizing 1.25 grams of each of the inhibitors, ortho, meta and para-nitrobenzaldehyde. Also included in each of the solutions was 25 ml. of ethyl alcohol. Subsequently, into each of the solutions, a rusty and a bright coupon were emersed for a period of 16 hours.

At the end of this time, no change was observed on the surface of these coupons.

Example VI Another series of experiments were utilized wherein bright, mild steel coupons were emersed in a variety of different solutions all of which contained 1.25 grams of para-nitrobenzaldehyde. The coupons were allowed to remain in these solutions at ambient temperature for 16 hours, after which they were removed, dried, and observed. In rating the surfaces observed after the experiments, an arbitrary scale ranging from 0-10 was established, with 10 representing a complete, uniform covering from the benzaldehyde-acid solution and 0 representing no covering at all. The results of this additional series of experiments are summarized below.

Acid or Acid Substitute Solvent Coating Coneen- Amount, Amount, Rating Kind traltiixon, ml. Kind ml.

Hydrochloric O. 25 25 NaOH 1. 0 25 Hydr0chloric 0. 5 25 Bromic 0. 5 25 Picric 0. 5 25 6 Trichl0roaeetic 0. 5 25 10 Having thus described the invention by providing specific examples thereof, it is to be understood that no undue limitations or restrictions are to be drawn by reason thereof and that many variations and modifications are within the scope of the invention.

We claim:

1. A solution comprising from about 1000 to about 3000 parts per million parts of solution of a compound chosen from the group consisting of meta and para nitrobenzaldehyde, and the lower soluble alkyl derivatives of said two nitrobenzaldehyde isomers, said derivatives being characterized by having not more than about 3 carbon atoms in the lower alkyl portions thereof, a solvent for said compound, and a sufli'cient amount of a strong, nonoxidizing acid to improve the corrosion retarding effect of said solution.

2. The solution defined in claim 1 further characterized in that said acid is present in the solution in a concentration from about 0.1 to about 3.0 normal.

Hb- H oococoeotorcqo co 3. The solution defined in claim 2 further characterized in that said acid is present in the solution in a concentration from about :25 to about 1.0 normal.

'4. The solution defined in claim 3 further characterized in that said acid has a dissociation constant of at least about 0.1.

5. A solution comprising from about 1000 to about 3000 parts per million parts of solution of a compound chosen from the group consisting of meta and para nitrobenzaldehyde, and the lower soluble alkyl derivatives of said two nitrobenzaldehyde isomers, said derivatives being characterized by having not more than about 3 carbon atoms in the lower alkyl portions thereof, a solvent for said compound, and a nonoxi-dizing acid having a dissociation constant of at least 0.1 present in the solution in a concentration from about 0.1 to about 3 normal.

6. The solution define-d in claim 5 further characterized in that said acid is present in the solution from about 0.25 to about 1.0 normal.

7. A solution comprising from about 1000 to about 3000 parts per million parts of solution of a compound chosen from the group consisting of meta and para nitrobenzaldehyde, a solvent chosen from the group consisting of ethanol and acetone and a suflicient amount of a strong, nonoxidizing acid to improve the corrosion retarding effect of said solution.

8. The solution defined in claim 7 wherein said acid has a dissociation constant of at least 0.1.

9. The solution defined in claim 8 wherein said acid is present in the solution in a concentration from about 0.1 to about 3.0 normal.

10. A method for forming a corrosion resistant coating on a metal surface which comprises the steps of:

immersing said metal surface in a solution comprising tfrom about 1000 to about 3000 parts per million parts of solution of a compound chosen from the group consisting of meta and para nitrobenzaldehyde, and the lower soluble alkyl derivatives of said two nitrobenzaldehyde isomers, said derivatives being characterized by having not more than about 3 carbon atoms in the lower alkyl portions thereof, a solvent for said corrosion inhibitor and a sufficient amount of strong, nonoxidizing acid to improve the corrosion retarding effect of said solution; and

maintaining said metal surface immersed within said solution for at least thirty minutes.

11. The method of forming a corrosion resistant coating on a ferrous metal surface which comprises the steps of:

immersing said metal surface into a solution comprising from about 2500 to about 3000 parts by weight of a compound chosen from the group consisting of metanitrobenzaldehyde and para-nitrobenzaldehyde per million parts by Weight of said solution, a solvent chosen from the group consisting of ethanol and acetone, vand an acid chosen from the group consisting of sulfuric and hydrochloric acid, said acid being present in the solution in a concentration from about 0.25 to about 1.0 normal; and

maintaining said metal surface immersed within said solution for at least 4 hours.

References Cited by the Examiner UNITED STATES PATENTS 1,548,495 8/1925 Van B'uhler 106--14 2,662,808 12/ 1953 Newschwander 21--2.5 2,965,577 12/ 1960 Heiman et al. 252-448 3,051,595 '8/ 196 2 Fullhart et al 1486.15

OTHER REFERENCES Funke et al., Werkstoife and Korrosion, 1958, I, pp. 202-16.

RICHARD D. NEVIUS, MURRAY KATZ, Examiners. ALFRED L. LEAVI'IT, Primaly Examiner.

R. S. KENIDALL, Assistant Examiner. 

11. THE METHOD OF FORMING A CORROSION RESISTANT COATING ON A FERROUS METAL SURFACE WHICH COMPRISES THE STEPS OF: IMMERSING SAID METAL SURFACE INTO A SOLUTION COMPRISING FROM ABOUT 2500 TO ABOUT 3000 PARTS BY WEIGHT OF A COMPOUND CHOSEN FROM THE GROUP CONSISTING OF METANITROBENZALDEHYDE AND PARA-NITROBENZALDEHYDE PER MILLION PARTS BY WEIGHT OF SAID SOLUTION, A SOLVENT CHOSEN FROM THE GROUP CONSISTING OF ETHANOL AND ACETONE, AND AN ACID CHOSEN FROM THE GROUP CONSISTING OF SULFURIC AND HYDROCHLORIC ACID, SAID ACID BEING PRESENT IN THE SOLUTION IN A CONCENTRATION FROM ABOUT 0.25 TO ABOUT 1.0 NORMAL; AND MAINTAINING SAID METAL SURFACE IMMERSED WITHIN SAID SOLUTION FOR AT LEAST 4 HOURS. 